//按钮的样式
@mixin btn($width:126, $height:36, $font:16, $bg-color: $blue, $color:white, $radius: 4) {
    background-color: $bg-color;
    display: inline-block;
    width: #{$width}px;
    height: #{$height}px;
    line-height: #{$height}px;
    border-radius: #{$radius}px;
    font-size: #{$font}px;
    text-align: center;
    color: #{$color};
}